Expose transaction::TransactionProgress as public

[boyswan]

Currently there's no submit_then_watch to work with offline signed Tx's - using sign_and_submit_then_watch requires the use of a signer.

By exposing transaction::TransactionProgress I can have my own implementation of submit_then_watch without being bound to signing in subxt.

async fn submit_then_watch<'client>(
    client: &'client Client<DefaultConfig>,
    ext_hash: H256,
    signed_tx: Bytes,
) -> Result<TransactionProgress<'client, DefaultConfig>, parity_scale_codec::Error> {
    let sub = client.rpc().watch_extrinsic(signed_tx).await.unwrap();
    Ok(TransactionProgress::new(sub, client, ext_hash))
}

let events = submit_then_watch(&api, ext_hash, signed_tx)
      .await
      .unwrap()
      .wait_for_finalized_success()
      .await
      .unwrap();

[jsdw]

Sounds good to me! Happy to accept a PR to expose this, otherwise I'll get around to it quite soon :)

[boyswan]

#401